In patients with cystic fibrosis, a defective gene and the protein it creates cause the body to produce unusually thick, sticky mucus that builds up in the lungs and the pancreas, leading to life-threatening lung infections and an impairment of the body's ability to properly break down and absorb food.

The drug, VX-770, is a pill that targets the defective protein. It showed sustained improvements in lung function of over 10% in patients with a specific gene mutation. The caveat, though, is that the specific mutation being targeted by the drug, G551D, affects just 4% of the CF population. But it's possible that the results of this trial will provide a basis for the use of VX-770 to treat other mutations. VX-770 is currently being tested in combination with another drug, VX-809, in people with two copies of the more common Delta F508 mutation.

In the trial, patients also showed improvement across all key secondary goals of the study, Vertex said, including decreased pulmonary and respiratory symptoms and weight gain (seven pounds on average). In addition, average sweat chloride (salt) levels, a key clinical indicator of CF, dropped toward normal levels, indicating that the drug is having an effect on the underlying defect.

VX-770 helps "open the gate" at the cell surface -- enabling the protein to pass through, as it would in healthy cells. This restores a proper flow of salt and fluids on the surface of the lung, the company explained.

"Treating the underlying cause of cystic fibrosis with VX-770 led to clinical improvements that were far beyond our expectations, providing support for an entirely new approach to the treatment of this disease," said Peter Mueller, executive VP of global research and development, and chief scientific officer for Vertex.

A Long Time Between Genetic Discovery and New Medicine

"These results are highly encouraging," said Robert Beall, president and CEO of the Cystic Fibrosis Foundation, which collaborated with Vertex on the drug development, including an approximately $75 millioninvestment. "They provide scientific evidence that support our long-standing belief that targeting the underlying defect of CF may have a profound effect on the disease."

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Cystic fibrosis is an inherited genetic disease that affects about 30,000 people in the U.S. and 70,000 worldwide, according to the Cystic Fibrosis Foundation. In the 1950s, few children with cystic fibrosis lived to attend elementary school. Today, patients can expect to live into their 30s, 40s and beyond. Still, very few treatments are available to CF patients, and those that are generally target the disease's symptoms.

But while this drug trial is being hailed a victory, it also highlights the problems of targeted therapy, as Mathew Herper of Forbes writes. "Cystic fibrosis is a symbol of how difficult it is to move from genetic discoveries to new medicines. The gene for the disorder, which causes patients' lungs to fill with thick mucus, was discovered in 1989 by Francis Collins, now the director of the National Institutes of Health. Yet treatments have been slow in coming."

Vertex said it will file for U.S. approval of the drug in the second half of this year. Analysts estimate VX-770 could, if approved, generate peak annual sales of some $600 million.